1. Field of the Invention
The present invention relates to the technical field of touch panels and, more particularly, to a multi-touch system and method for controlling liquid crystal capacitors to reduce touch sensing interference.
2. Description of Related Art
Typically, the capacitance changes of liquid crystal capacitors CLC in liquid crystal displays (LCDs) are used to achieve a display on the panels. The change of a liquid crystal capacitor is varied with different voltages to thus have the corresponding values. FIG. 1 is a graph of capacitance CLC vs voltage V for a liquid crystal capacitor. In FIG. 1, the voltage V is changed from zero to 5V. The relationship between capacitance CLC and voltage V is obtained by controlling the voltage V as shown in FIG. 1.
Accordingly, when the capacitance of the LC capacitor CLC on the LCD panel is changed, a capacitive touch sensing is operated, which is likely to cause a touch sensing mistake. FIG. 2 is a schematic diagram of a typical capacitive touch sensing on an LCD panel, where Cp indicates a finger capacitance. The touch sensing detects a capacitance change between the finger capacitance Cp and the touch panel or LCD panel. In this case, whether an out-cell, on-cell, or in-cell capacitive touch is affected by the liquid crystal capacitor CLC of the LCD panel.
FIG. 3 is a schematic diagram of an in-cell touch sensing of a liquid crystal capacitor, where Cp indicates a capacitance produced when a finger touches on the LCD panel, and CLC indicates capacitance of the liquid crystal capacitor. Since the pixels are displayed with different values, there are different voltages for the liquid crystal capacitors CLC through the source driving lines. Thus, it is known that capacitance of the liquid crystal capacitor CLC is varied with the pixel values as shown in FIG. 1. Namely, capacitance of the liquid crystal capacitor is not a fixed value. When capacitance of a liquid crystal capacitor is not fixed, it is difficult to perform a capacitive detection because the finger capacitance Cp is connected to the capacitor CLC and change of its capacitance change is small, resulting in that the influence of the capacitor CLC is significant.
However, the capacitive touch sensing technology detects the change of the capacitance Cp to determine whether a finger touches the panel. FIG. 4 is a schematic diagram of a typical capacitive touch sensing technology. In FIG. 4, the capacitance Cp between the finger and the sensing electrode is produced, and the change of the capacitance Cp is detected to obtain the information of the touched position of the finger. Since the change of the capacitance Cp is small, it is sensitive to noises, and a wrong decision may be made. Thus, when the touch panel is mounted on the LCD panel, it is likely to be affected by the noises produced by the LCD panel.
A method is to add an insulating sheet or air gap between the touch panel method to thereby prevent the noises of the display panel from interfering the touch sensing. However, in addition to the increased cost or panel thickness, such a method can be used only in the out-cell touch technology. Moreover, the noise isolation from the display panel is not satisfactory. Another typical method is to boost the driving voltage for increasing the SNR, which may overcome the noises but consume more power.
In the capacitive touch technology, if capacitance of the liquid crystal capacitor CLC is not fixed, sensing a capacitance Cp becomes difficult, and then a wrong decision may occur. As shown in FIG. 5, when the liquid crystal capacitors CLC are changed while a typical touch sensing is performed, it causes a reduction or increase of the raw data extracted on touching, resulting in making a wrong decision and coordinate sway.
Therefore, it is desirable to provide an improved multi-touch system and method for controlling liquid crystal capacitors to reduce touch sensing interference, so as to mitigate and/or obviate the aforementioned problems.